The present invention relates to systems, such as a powertrain or a continuously variable transmission, that provide greatly improved speed control, torque transfer, fluid control, and lubrication by using an epicyclic gear set, a hypocycloid gear set and the like as a fluid pump and achieving infinitely variable control of the output shaft to input shaft rotational speeds (speed ratio) of the gear set by controlling fluid flow through, or pressure within, the fluid pump.
The use of a gear set like an epicyclic gear set to change output to input torque and speed ratios is common in many powertrains whose output and input shafts are on the same centerline because of compactness and a high torque capacity. Torque is transferred through the mechanical engagement of gear teeth. If a speed ratio change is desired, the gear set is engaged or disengaged, thereby generating a step change. Multiple gear sets have to be stacked to generate many small step changes between the minimum and maximum desired speed ratios at the expense of compactness.
I have recognized that an infinite speed ratio control between fully engaged and fully disengaged modes of gear sets like epicyclic and hypocycloid gear sets can be achieved by using the gear set as a fluid pump so that the speed ratio is controlled only by the internal pressure.
The present invention employs the novel principle that, if the relative rotational speed between any two of the three main rotating components (ring gear, planet carrier, and sun gear) of an epicyclic gear set is controlled, the overall speed ratio of the gear set can be controlled. The use of a fluid pump run by the gear set's rotating components is thus a simple and novel way to infinitely control the output shaft speed to input shaft speed ratio.
If, on one hand, the fluid is incompressible in a fluid pump and the pump's fluid flow outlet is closed, the pump is hydraulically locked. The pump drive gears then are prevented from having relative motion, and the entire gear set rotates as one unit, generating a 1:1 speed ratio. On the other hand, if the pump outlet is completely opened so that there is no fluid pressure, all gear set components are uncoupled so that no torque is transferred between the input and output, generating a speed ratio of 0. Fluid pressures between fully open and fully closed then control the gear set speed ratio. This has been shown using bulky external fluid pumps as disclosed, for example, in U.S. Pat. No. 6,688,851.
More advantageously, the present invention uses the mechanical power transfer gear set as the fluid pump to regulate its own speed ratio, thereby creating a very compact and self-contained infinitely variable power transfer device requiring very few components. The present invention provides the ability to engage a single gear set with infinite variability between its minimum speed ratio (no fluid pressure) and maximum speed ratio (hydraulically locked).